1. Field of the Invention
The present invention relates to a laser beam machining apparatus and, more particularly, to an apparatus used for wire cutting and wire joining on a liquid crystal board or a liquid crystal panel in manufacturing a liquid crystal display.
2. Description of the Related Art
Conventionally, a laser beam machining apparatus for performing wire cutting and wire joining on a liquid crystal board or a liquid crystal panel comprises a laser beam source, an irradiation optical system having a laser irradiation function and microscope function, and X-Y stage for holding the liquid crystal board or the liquid crystal panel.
In the laser beam machining apparatus of this type, it is very important to increase the laser machining accuracy, to achieve homogeneous machining and to prevent the occurrence of the machining faults. Therefore, for example, after transmitting a liquid crystal element composed of many liquid crystal cells, a laser beam is reflected by a polarization beam splitter, and only the selected polarized component of laser beam is converged and irradiated on an object being, for example, a wire pattern of the liquid crystal cell, machined via an objective lens. Also, the film thickness distribution of the object being machined is measured beforehand, and a proper voltage is applied to each liquid crystal cell of the liquid display element so that the optimum power density for machining the film at the machined position will be obtained. Thereby, the transmissivity of each liquid crystal cell is adjusted, and the laser beam having the optimum power density is irradiated on the object being machined.
This technique has been disclosed in Japanese Patent Application Laid-Open No. 4-288988. With the technique described in this Publication, even if the thickness of a metal film formed on a liquid crystal board is nonuniform, this metal film is removed completely by a laser beam without producing damage to a base.
In performing wire cutting and wire joining on a liquid crystal board and liquid crystal panel, however, fine machining of wire having a wire width on the order of submicron and a length 50 times or more the width, square machining of 2 .mu.m, and the like are performed. That is to say, it is required to perform machining an object having a region to be machined with a greatly different length-to-width ratio. In this case, in the conventional laser beam machining apparatus, the repeatability of machining cannot sometimes be maintained uniformly at some angle of the fine wire to be machined because of the influence of polarized state of the irradiated laser beam.
Also, when a wire within a liquid crystal panel is machined, a laser beam especially of a visible wavelength zone is immediately absorbed and attenuated by a polarizing plate affixed to the panel surface, so that the homogeneity of machining quality deteriorates.